1. Field of the Invention
This invention relates to a process for making N-vinyl lactams, and, more particularly, to a single stage process, with recirculation, for making N-vinyl pyrrolidone or N-vinyl caprolactam at a high reaction rate and selectivity and at a predetermined conversion per pass.
2. Description of the Prior Art
The reaction of acetylene with a lactam in the presence of a catalytic amount of an alkali metal salt of the lactam to produce N-vinyl lactams is well known in the art. Generally, the conversion of 2-pyrrolidone, for example, is about 30 to 62%, and the selectivity is less than 90%. Attempts at higher conversions usually result in formation of non-volatile polymer residues which are difficult to separate from the desired product.
Parthasarathy et al, in U.S. Pat. No. 4,410,726, described a similar process using crown ethers (polyoxyalkylenes) as a co-catalyst in the vinylation reaction to increase the selectivity and reaction rate. However, the yield is only 70% and substantial amounts of polymer residues needed to be separated from the N-vinylpyrrolidone, unreacted 2-pyrrolidones and other by-products.
Liu et al, in U.S. Pat. No. 4,873,336, disclosed the use of potassium t-butoxide as a catalyst in the vinylation process which provided a 62% conversion and 90% selectivity.
Chu et al, in U.S. Pat. No. 5,665,889, described the use of ether oligomers or diols as a co-catalyst in an attempt to increase the yield of vinylpyrrolidone and decrease the production of by-products.
Schmidt-Radde et al, in U.S. Pat. No. 5,670,639 described a vinylation process using aqueous KOH in the vinylation.
While these and other prior art processes can increase the rate of vinylation by an increase in the reaction temperature and/or catalyst concentration, these physical changes lead to an increased amount of by-products. Furthermore, such processes are hazardous because gaseous acetylene at high pressures advantageous for high reaction rates may decompose spontaneously.
Accordingly, it is an object of this invention to provide an improved process for making N-vinyl lactam by reaction of acetylene with a lactam in the presence of a catalyst.
Another object herein is to provide a single stage process, with recirculation of the reaction mixture for making N-vinylpyrrolidone or N-vinyl caprolactam at a high reaction rate and selectivity and at a predetermined conversion per pass.
A feature of the invention is the formation of a reaction mixture by saturating a non-aqueous, liquid mixture of lactam, vinyl lactam and catalyst with acetylene at low temperatures and pressures to provide a high concentration of acetylene in the liquid.